Dealuminated heated clay as new fluoride adsorbent for treatment of contaminated drinking water

Abstract

The present study aims to reduce the fluoride concentration of drinking water using a novel mild adsorbent based natural clay. The natural clay was dealuminated/realuminated and dehydroxylated by intense washing and heating processes. The developed adsorbent was confirmed by X-ray diffraction (XRD), thermal analyses (ATD-TG) and nuclear magnetic resonance solid-state with magic angle spinning (MAS NMR). MAS NMR results showed that distorted tetrahedral-Al coordination and penta-Al coordination sites were responsible for fluoride adsorption. Batch adsorption experiments were investigated without any adjustment of water pH. The effect of the clay dosage over the range of 0.5–2 g/50 mL of sample solution was studied. Results revealed that the aggregation of the clay particles in the water was successfully avoided thanks to the heating process. Kinetics and adsorption isotherms were also investigated. The adsorption equilibrium was achieved on a timescale of seconds. Adsorption kinetics data followed pseudo-first-order as well as pseudo-second-order models while isotherm experimental data followed the Freundlich model. The maximum adsorption capacity was relatively small (1.2 mg${\cdot }$g$^{-1}$). Tests performed on Tunisian contaminated drinking water showed that water potability with respect to fluoride was successfully achieved; suggesting that the dealuminated/realuminated dehydroxylated clay can be a promising fluoride adsorbent for drinking water.

Keywords

• Dealuminated heated clay
• Adsorption fluoride
• Kinetics
• Isotherm
• Drinking water